US2421106A - Airway traffic control system - Google Patents

Description

May 2?, E947. 1s. N. www ET Al.

AIRWY TRAFFIC CONTROL SYSTEM 5 Sheetsfheet l Filed Jan. 21, 1943 OMMO( v. nventcr mwgh-t and 0.5mm a THEIR Gtorucg S. N. WRGHT ETAL AIRwAY TRAFFIC CONTROL SYSTEM Filed Jah. 21, 1945 3 sheets-sheet 2 IIIIIIIIIIIIIII-llllll llilllllllllllllllllllllllllliillll E?, E94?. s. N. wlan-rr Erm. A

mmm' TRAFFIC common sYs'rEM Filed Jan. 2l,- 1943 3 Sheets-Sheet 3 Patented l www: invention relates to c '1-r -r" its. thi) ident-'imm m' thealtitude of airplanes.

l mchaixplanes w travel over spediled ma rm at ied altitudes on various stretches it is essential that the whereabmzts of airplanes already given authorization to m in the vicinity be definitely known.l Although pilots of airplanes living over commercisl air routm are seldom lost because radio range legs or courses guide them over the grolmdy route, radio mes and radio ian markers inform them when tmy have reached certain cheek- Doints or stations along the air route and altimeters inform them of their altitude,` there is a possibility that a pilot may not know what radio il" he is passing over. For reasons of safety, the should be iniormed of the location, identity and altitude of each airplane by meellenica: and electrical apparatus automatically so that wrong indications or reports due to failure of the human element are avoided.

In view of the foregoing and other considerations. it is proposed in accordance with the present invention to pmvlde apparatus. at each radio iin, check-point or ground location, which by radio commmiosting apparatus will communicate with airplanes yins over auch particular check-point only at one altitude at a time. so that if a plurality ci airplanes ily over the same check-point at diflerent altitudes. as is possible,

such radio can be established with only one i i at a time, thereby avoidins the possibility or a mutilated code or other interierence.

More specically, it is further proposed to mit the information, of airplane identity. airplane altitude and check-point identity. from such check-point location to a centralised dispetchers omce and to tm retransmit informae at which he is living and is mins over, so that the me entr-soins pilot not only has the check-point speciiically dlspatcnmg of airplane traine. bv

(Ci. rfb-$58) asecondtime duringasingleiilshtoverthe check-point or other ground location.

Another object oi. the pmt invention resides in utilizing the check-point located apparatus for transmitting the answer-bach message the central omce to the pilot of the airplane.

Another object oi the present invention resides i'n the provision of means for preventing the check-point located apparatus from communicating with a second airplane until the complete answer-back infomation for a first airplane has been transmitted from the central omce back to the pilot of such airplane.

Another object o! the present invention resides in the provision oi mechanism at the check-point ground location for determining which one of a plurality of airplanes flying at different altitudes over auch location at the same time shall be first to communicate with the dispatcher-'s .omce through the medium of the check-point ground located apparatus.

Another object oi the present invention resides in the plovlfslon of code creating, code repeating,-and decoding mechanism for transmitting by code the aforementioned information between the airplane and the dlpatchers ollloe.

Other objects. purposes and characteristic features o: the present invention will in part be pointed out in the speciiication hereinafter and will in part be obvious from the accompanying drawinssinwhich:

Figs. 1A and 1B show the airplane carried apparatus, the apparatus located at a check-point and a portion of the apparatus located at the dlspatchers olllce: and

Fig. 2 shows a time chart illustrating the sequenoe of operation oi the various devices oi the apparatus illustrated in Figs. 1A and 1B.

Structure.Referring-to Fiss. 1A and 1B of the drawings, apparatus has been illustrated therein to show one embodiment of the present invention which apparatus is located at three different places, namely. on the airplane designated "Plahe by suitable legend, at the checkpoint location CPS, shown by dotted lines, and at the central oilice or dispatcher's olilce DO also shown by dotted lines. On the airplane. as illustrated, are shown a pilot's radio transmitterreceiver PIR. which ai'l'ords direct two-way radio communication between the pilot and the dispatcherc oillce or some operator under the dispatcher's Jurisdiction, and in addition to this pilots radio PIR therein provided an airplane receiver PR and an airplane transmitter PT for the' purpose of automatically communicating fioul.

scenico i which is derived through the noch contect if the relay OCR?. These of tedio carrier 'requency energy have superimnosed thereon, hat is, are modulated ny tone frequencies eenerated by the tone generators 2T to 21T inclusive, )ne at e, time. That is, e tone pulse comesooncl- ,mz to tone generator 2T is mst emitted by the interina, ATi superimposed of course unen the :entier frequency, which is then followed by tone puke and then by tone pulse d, end so on un-u ill ell of the tone pulses 2 to il have been transnltted, after which this cycle is repented.

Let us now essunie that the dirplane Plane (see Fie. iii) gets within the renee of the radio :eem transmitted by the ent/enne, ATi, it being inderstoocl that the radio frequency is such and ;he antenne. so designed that this radiation 4of redio waves by the antenne AT5 is directed meinm ly upwardly through e, limited angle of spread so that en airplane must he almost directly over u the check-point in order to respond to the ref :listed energy. Thot is, in practice, the airplane remains in communication with the check-point apparatus only for about one-half minute during its flight over the check-point.

Let us now assume that the airplane Plane is dying at an altitude of 2G00 feet end that its eltimeter contact il is in engagement with ste.- tionary Contact 2 of the altimeter .elli/I. Under this condition the eirplane receiver PR is receptive only if rudio Waves of the proper irequency are emitted by the antenne ATi and then only ii they are moduleted at the rate oi modulation effected by tone generator 2T. On the next rotation of the scanning Contact iii when it reaches the stationery contect of he altitude scanner AS, the energy transmitted by the transmitter CPT through the medium of the antenna ATi to the receiver PR will cause the relay TR carried by the airplane Plane to pick up and by the closing of its front Contact dil closes en energizing circuit for the motor This causes the motor M3 tc operaie and close s. sticlr circuit for the stick relay TRP including the commutator contacts PCi and stick Contact li. Rotation of the coding cem PC3 in aclockwise direction results in the closure of Contact i@ of the eirplane transmitter PT which results in the transmission of radio frequency energy impulses from the antenna ATS to the antenne ATli resulting in the picking up oi' the relays CR and SR. The picking up of the relay ESR closes its front com tact 33 thereby energizing the loch. :relay LR and causing the latch wheel LW to be held in its contact 2 position by the latch iii, in which position the rotary erm 2E! still engages the ste.- tionary contact segment 2 of altitude scanner AS. Energization of the loci: magnet LR by the opening of its Contact 2li. of course deenergizes the clutch magnet CM and removes the application oi torque to the scanning shaft .22. It is thus seen that the clieclpoint apparatus continues to transmit radio frequency energy modulated at the same rate as before from the transmitter CPT to the receiver PR on the airplane.

Referring now to Fig. 2 the picking up of the relays TR and T'RPP on the airplane is indicated by the rise in graphs 62 and 53 whereas the picking up of the relays CR and SR and the energization of the lock magnet LR is indicated 'by the rise in graphs f, B5 and 55, respectively. The relay CR will of course follow the code transmitted by the coding cam C and this code consists of four impulses followed icy three irnpulses followed by two immusee es indiceted by r PCi reclose.

the humos on coding wheel and. icy clashes in Fien 2 or the drawings This codo receivingf reley CR then repeats these impulses through the medium oi? its contact by intermittent energization of 'the code receiv ing relay GCR located in the dspetchers cnice DO. It will he seen that this code receiving reley CCR through the medium of its front con tacts di will cause the received code to he retransmitted to the ciro-iene hy the intermittent energization of the relay @CRP ond the intermitteilt opening of its loool; conte ,t 38, which Contact ri feeds tone energy to the radio trains mitter CPT. In other words, es indicated by graph t2 in Fig. Z of the drawings the code transmitted by the airplane to the oiice is repent/ed beck to the airplane by en o' period for erich on" period of the ground located releys es shown by graphs trl, 'lli and EiB representing the relays CR, OCR and @CRP in Fie. 2 of the drawings.

Let us now observe more speciiicelly how the coding motor M3 on the airplane is energized end how it is deeners'ized after the coding cem has made one complete revolution. Referring to Fig. lA the originel picking up of the relay TR causes energy to loe applied through thel inediurn of its frontcontact Bil through e circuit including the motor M3 and 'the front contect l@ of the relay TRP. As soon es the coding shaft has turned through a small angle, end before the slow dropping relay TRP has had en opportunity to drop, the commutator contacts lYCi and PC2 are both closed thereby closing d stiel-r circuit for the relay TRP including the contact PCi and also including the sticlr contact il of the relay TRP. The motor Mil is now also energized through another or auxiliery circuit cludine the front contact lil of the relay TR? and including the commutator contact PCT?. This auxiliary circuit for the motor iiil is provided so as to cause continuous operation of the `motor M3 in spite of intermittent deenergization and dropping of the relay TR.

The relay TRPP is energized each time thet the relay TR is picked up and is also energized so long es the motor Mt is energized, so thatthis relay TRPP will assume its energized position as soon as the coding motor M3 is initiated into operetion und will remain either continuously or intermittently energized until the relay TR is permanently deencrgizcd. This relay TRP? is so slow dropping that it will not drop its contacts after complete deenergizetion of its windings uil-- til about one-half minute of time has elapsed. In practice this cannot be readily done by u relay of the ordinary construction and a special timing relay including a dash-pot or other suiteble time delay means may be employed, if desired. When the motor has operated the coding Wheel FC3 through its entire revolution the Stich circuit for the relay is broken et the commutator contacts PCi thereby causing deenergization of this relay TRP and causing deenergizaition o the motor M3 before the contacts The relay TRP will not seein. he picked up until the slow dropping relay TRP? has assumed its dcenergized position, which requires about one-half minute, this by reason of the fact that the nich-up circuit for the relay TRP includes the beck. contacts i3 of the relay TRPP and. lf3 of the relay TF, in series. In prectice, as already pointed out, en airplane is not within the radiating range of 'the transmitter CPT et e, checisqioint for more than about helrninute and since the slow dropping rele-y 'Ii'RPlP d requires about a half-minute period to be operated to its deenergized position the airplane apparatus of a particular airplane can only get into communication once during a flight over a checkpoint radio transmitter.

Referring again to Fig. 2 of the drawings time has now elapsed as indicated by the nine dashes 58 representing the airplane identifying code and this code has not only been transmitted to the dispatchers omce as indicated by the jcgged graph till signifying the operation oi the relay CR and received at the dispatchers orilce as illustrated by the logged graphs lil and et illustrating the operation oi the code receiving relays OCR and OCRP located in the dispatchers oce and checkpoint respectively, but has also been retransmitted baci: to the airplane as indicated by the joggecl graph t2, signifying the operation oi the relay Tft constituting part of the receiver PR located on the airplanePlane. This code is repeated into the pilot's earphone PHS through the medium of contact i5 of the relay TR.

Referring again to Fig. 2 it will be observed that altitude relay A2 has now been energized as indicated by the graph ill and that the picking up of its contact 23 has caused deenergization of the relay AP. However, by reason of its slow dropping characteristic, as indicated by the shaded portion of the graph ll, this relay AP has not yet assumed its deenergized position. Dropping of the stick relay TRP has, however, taken place and this is indicated by shaded portion ci the graph lil of Fig. 2 of the drawings. In regard to the picking up of an altitude relay. such as the relay .A2, this relay is slow to piclr up, as conveniently indicated, and will not nichF up during rotation of the contact arm 2b but will piclr up if this contact arm stops on one of the stationary contact segments,

As thus far described the check-point located apparatus Cris has scanned the area directly above this location, and has found an airplane iiying at the u@ foot altitude, causing the scanner to stop on the contact segment 2 and resulting in the reception oi radio Waves by the air plane having e. tone signifying the 20D() foot altitude superimposed thereon. This resulted in the lock, magnet LR being magnetized which caused the apparatus on the airplane Plane to transmit a plane identifying code consisting of four impulses followed by three impulses, followed by two impulses and the coding apparatus on the airplane has completed its cycle and has again been brought to a stop,

As already pointed out the relay AP is very slow dropping, as indicated by the heavily shaded portion of line lll, and was held up throughout the entire transmission of the airplane identifying code to the dispatchers oce and back to the airplane. This relay AP has now reached its deenergized position as a result of which its back contact El has completed an energizing circuit through the motor Mt and including the front contact til of the stick relay APP. As soon as the motor M2 has operated the coding shaft bil through a small angie a stick circuit for the relay APP is closed including the back contact 2l of the relay AP, the commutator contact CPC and the stick contact 2t? oi this relay APP. The motor Mt will nowcontinue in operation until the coding shaft tu, driven through suitable gears (not shown), has completed one complete revolutlon at which point the stiel; circuit for the relay APP is broken at the commutator contact CPC. During this revolution of the coding shaft i3@ the radio fix coding cam CPF', ior identify the radio hx or checl-point at which it is local will transmit code elements to identify t check-point, which consists ci four pulses in present instance. rThis is followed by a series pulses identifying the altitude at which the a plane is ilying, which in the present instance ci sists of two pulses, wul be transmitted by i coding cam CP2 because the altitude relay now assumes the energized position and ali the other altitude relays Ai-Ail assume their i energized positions.

It will be observed that the humps on the c ing cam CP2 do not overlap with the humps the coding cam CPF sc that the four impul` created by the cam CPF will be followed by i two impulses created by the coding cam CP2. T code will cause intermittent picking up and dr( ping of the code following relay GCR, in the d patchers ofllce BO through a circuit which m be traced from the positive terminal of a sou; of current through baci; contact 223 of the rei AP and ythrough thc contact CF controlled the coding cam CPF and through a multi; branch circuit also including this back cont-z 2d of relay AP and front contact 25 of relay and further including the contact C2 of the cc ing cam CP2 and from there on these two multi; circuits converge into one circuit including i line wires 3l and the code following relay O( located in the dispatchers oirice. This code co ,sisting of a group oi four impulses identifyi the radio x, followed by a group of 'two impuls identifying the altitude at which the airplane ilying, is indicated by the dashes 59 in Fig. 2 the drawings. it will be observed that these cc impulses result in corresponding picking up a: dropping of the relays OCR and OCRP as shoi by the graphs l5 and El? of Fig. 2 and is also i dicated by corresponding oil periods in the e ergizing circuit for the relay TR as indicated the graph t2 in Fig. 2 of the drawings.

Referring to Fig. iB it will be observed tl". the code transmitted from 'the airplane to the d patchers ofiice and consisting of an airplane ide tiilcation code cannot overlap or interfere wi the code transmitted by the coding cams Cl and CP2 because the lrst of these codes is trar mittecl through a circuit including the front co tact 2d of the relay AP whereas the second me tioned code is transmitted through a circuit i cluding the contact 28 in its deenergized po tion.

Referring now to the graph it in Fig. 2 of t drawings, this graph shows that the relay Ol was picked up in response to the ilrst code i1 pulse transmitted to the dispatchers omce manifested by the relay OCR and was not dropp until the last element of the complete code h been transmitted, and that the relay K controll by this relay ODC repeats this same operation the check-point location. This is shown in Fig by the graph ill. By referring to Fig. 2 it will observed that the apparatus at the check-poi and on the airplane is not returned to its nc mal condition immediately after the entire co has been retransmitted to the airplane ev though the apparatus located in the dispatche cnice is. This is due to the fact that the pa ticular altitude code which was assumed to ha been transmitted was a two-impulse code sigr tying an altitude of 20ml feet and for this reas the coding shaft il@ had not completed its rot tion and this idle rotation ci' the shaft Si is inc lradio transmitting apparatus located at the check-point or radio nx location.

It should also be understood that, ii desired. instead of having the airplane receiver PR rendered responsive only to radio transmission of a particular radio frequency modulated to a particular tone that this response may be through the medium oi particular radio frequencies alo'ne and irrespective oi tone current modulation. The tuning of the receiving apparatus PR would be accomplished in this case through the medium or' a contact similar to the contact il on the alti meter. In other words. instead of using one radio carrier frequency and a plurality of tone irequencies a plurality oi radio carrier frequencies without having a tone frequency superimposed thereon may be employed, if desired. Since the conventional showing would be the same no additional drawings are deemed necessary.

The applicants have thus shown and described one particular embodiment and slight variations of their invention and one manner in which their invention may be employed, and have disclosed this invention in amore or less conventional manner. It is therefore desired to be understood that this has been done because radio communicating apparatus is well-known in the art and detailed circuits and apparatus including amplier, rectifier and detector tubes are so well known in the art that speciilc disclosure thereof is considered and believed unnecessary and it should be understood that the particular apparatus shown and described has been selected to show the nature of the invention and has not been illustrated to show the exact construction preferably employed in practicing the invention and it should be understood that various changes, modifications and additions may be made in practising the invention, so long as these changes come within the scope of the following claims.

What is claimed as new is:

1. In combination with ground station located radio transmitting apparatus, of means operatvely coupled to said radio transmitting apparatus for successively emitting radio beams characterizing different altitudes, airplane carried radio receiving apparatus having tuned means adjusted to respond to such radio beams one at a time, and altitude responsive means operatively coupled to said airplane carried radio receiving apparatus for adjusting said tuning means of said radio receiving apparatus to respond only to a radio beam characterizing the altitude such airplane is flying at at thattime.

2. In combination with ground station located radio transmitting apparatus, of means operatively coupled to said radio transmitting apparatus for successively emitting radio beams characterizing different altitudes, airplane carried radio receiving apparatus having tuned means adjusted to respond to such radio beams one at a time, altitude responsive means operatively coupled tosaid airplane carried radio receiving apparatus for adjusting said tuning means oi said radio receiving apparatus to respond only to a radio beam characterizing the altitude such airplane is flying at at that time'l and means to cause said radio transmitting apparatus to continue for a limited time to emit a radio beam liti characterizing a particular altitude if the airplane carried radio receiving apparatus has been adjusted by said altitude responsive means to such altitude adjustment and has responded to the initial radio beam characterizing such altitude.

3. In combination, a central oiice, a ground station, an airplane carried apparatus, code creating means included in such airplane carried apparatus for transmitting by radio a code identifying such airplane, code creating means at such ground station having its operation governed by transmission of said airplane identifying code for generating a code identifying such ground station, communicating means controlled by said code creating means for transmitting both of such codes over line wires to said centrai oiice in non-overlapping succession, and radio communicating means for retransmtting over a distinctive channel both of said codes from said central oiiice to said airplane carried apparatus.

4. The combination of interrelated radio transmitting apparatus at a check point ground station and radio receiving apparatus carried by an airplane, interrelated radio transmitting apparatus on said airplane and radio receiving apparatus at said ground station. of means including the radio transmitting apparatus at said ground station for successively emitting radio beams characterizing different altitudes, airplane carried altitude responsive means for adjusting the airplane carried radio receiving apparatus to render it responsive to a radio beam emitted by the ground station located radio transmitting apparatus characteristic of the altitude the airplane is -flying at at that time as manifested by such altitude responsive means, means responsive to the reception of a radio beam initiated by said airplane carried radio receiving apparatus and emitted by the airplane carried radio transmitting apparatus and received by the radio receiving apparatus at said ground station for causing the radio transmitting apparatus at such ground station to continue to transmit the last transmitted radio beam for a predetermined period of time, and means on said airplane for transmitting information to such ground station identifying said airplane through the medium of the radio transmitting apparatus on said airplane and the radio receiving apparatus at said ground station during said period of time.

5. The combination of interrelated radio transmitting apparatus at a check point ground station and radio receiving apparatus carried by an airplane, interrelated radio transmitting apparatus on said airplane and radio receiving apparatus at said ground station, of means including the radio transmitting apparatus at said ground station for successively emitting radio beams characterizing different altitudes, airplane carried altitude responsive means for adjusting the airplane carried radio receiving apparatus to render it responsive to a radio beam emitted by the ground station located radio transmitting apparatus characteristic of the altitude the airplane is ying at at that time as manifested by said altitude responsive means, means responsive to the reception of a radio beam initiated by said airplane carried radio receiving apparatus emitted by the airplane carried radio transmitting apparatus and received by the radio receiving apparatus at said ground station for causing the radio transmitting apparatus at such ground station to continue to transmit the last transmitted desinee o beam for e. predetermined period oi time, ns on seid sirmione for transmitting intorion to such ground station identifying sold iene through the medium ci the radio trousing apparatus on seid airplane ood tice recio ivino oppcrotus et seid ground station dursuch predetermined time. sind means et seid 1nd stetion for tlirough the medium oi seid um station located radio transmitting sono is and scid eirplane ,carried redio receiving aretus trensrnittins,J inforniotion identifying round station. in comblnotion, e ground stotion loceted lo transmitting opperetus, e ground station Yted radio receiving apparatus, airplane cor redio receiving e-nperdtus and airplane :led rudio transmitting apparatus, of ineens 11s-.tively associated with. seid ground station ted tedio treinsmitting apparatus i'or ecus such apparatus to successively emit soffice lotions each characteristic ci e, different eltie, airplane ccrried menos including scid airie carried receiving oppor-ctms for cousine the ratively associated eirpiene corrieri space lotion transmitting apparatus to transmit o ce radiation when the operatively associeted :lane corrieri radio receiving apparatus reres o space rcdietion characteristic oi the sitie the airplane is theo flying ot, end ground ited code communicating apparatus for transting to o distant point o code chorocteristic that altitude in response to the reception of ce radiation by the ground located radio re- ,fing apparatus from such airplane corried io transmitting apparatus. in e, system i'or automatically reporting the entre and identity of airplanes flying over e. und station; equipment on eec'n. airplane in- :ling radio transmitting means, e code senddevice and means coupling them together so to when rendered cective transmit s radio le signal identifying tiret airplane; receiving iaratus et s, ground station responsive to such lio code signal for when received communicatthat code signe-.l to e distant control oiice; i means partly ot seid ground stotion ond rtly on euch of e .plurolitg ci passing airplanes i ir'lcludinnY the transmitting means on such ,rclity of eirpiones slid solo' receivingJ oppersfor rendering seid equipments o'o said oir- .nes eiective only one et o time in o sequence ed by the respective eltitudes oi seid airplanes that time. i. in e system of the character described ior iorting the passage of airplanes over o, ground tion; tronsmitting'meens nt the ground ste.- n normally radiating; in limited aree over d station o, carrier' frequency having distincc tone modulations relating to different nitiies automoticolly applied thereto successively e at o time; moons on en eirplsne including a, :lio receiver, e. radio transmitter ond en mtim er means for transmitting on e diiierent freency a reporting eignsl for o limited time only the modulation of tlie cerrler frequency rodiz by seid ground stetion transmitting nieens rresponois with the altitude et which t ot eirme is then flying es manifested by seid sitimer means; and menos including radio receiv-w g equipment et the ground station responsive said reporting signal and including communiting concretos for automatically eonimunicet g to e, distont control oilce on indication monisting the nascose suon eirolcne ot suoli ',itude.

lli

9. lin e, oyster-n for eutozneticeily reporting to c, distont control oilice the vnascose of airplanes over o ground station, transmitting means at the ground ctetion normally ooeroting to radiate upwardly throughout o zone ci limited extent o piurelity or radio lieems oi distinctive conrector one et o time in succession to designate diiierent altitudes, radio receiving opperatus on @zich airplone eutorneticelly odjusted to be responsive to only one o1 seid radio beams novit-lg the choreoter corresponding with the altitude at which that airplane is tl'ien flying; radio frequency transmitter on the airplane having' its operation initiated by the response oi seid receiving or porotos for radiating ier limited time o, reporting sienel, und means et the ground stetion responsive to seid renoiting signal, whereby e. plurality of ail-plenos that may be passing over a, ground etntion at different altitudes will report their 'passage one et o, time es the ground station transmitting menno successively creates the radio beams of the distinctive characters corresponding with the respective .altitudes et which these eirplenes ore flying.

1G. A system 'lor reporting the identity und ps, sage of airplanes over o ground station compris ins', transmitting means et tile ground station for radiating over ein oren oi' limited extent shove the ground stotion o plurality of distinctive rcclio beams relating to different altitudes one et o time in succession, o radio receiver on each airplane for operating en electro-responsive device, ineens including mi eitimeter for controlling seid re ceiver to conse operation ci the electro-responsive device onlyr in response to one distinctive radio boom correspomlincl with the altitude at which the airplane is then flying', means on each aim-.lione including c radio transmitter and c. coding device .having its operation initiated by seid electro-responsive device for transmitting for e limited time e. reporting signal including an oirplerle identifying code, ond means at said ground stotion for receiving seid reporting signal and transmitting; t to o distant control office.

il. lin o, system for outomoticully reporting;r at e distant point the psege o airplanes over a ground station, rodio transmitting moons et the ground stotion including o scanner device normally rediotine' upwardly over e limited ares. e. plurality oi initie-,ting rudio seems oi distinctive characters relating to different altitudes one at o. time in succession, e. normelly inactive radio transmitter on each airplane operable when set into operation to send automatically a reporting signal for e limited time, moons on the airplane for initiating onerotion of seid transmitter in response to the reception oi an initiating radio boem having the clncrecter corresponding with the altitude et which the oil-plone is then flying, ond ineens ot the ground station responsive to seid reporting siunels for transmitting to a distent point n code signol conforming with `the position of the scanner device et tile time a reporting signe-l received, whereby the altitude oi esclu pessime' airplane is communicated to the dictons control point.

i2. "in on eutomctic airplane reporting system of tire character described, transmitting opparotus ot el ground static-n including e rotary scanner normally operating to radiate upwardly over o zone of limited ores e. carrier wave modulated with o plurality of distinctive tones one at o time es the econner roto/tes, means on ou airplone including en altitude detecting device for sending o radio signet on o diner-ent irequency paratus in response to the reception of a space radiation characteristic of the altitude in which the piene is then travelling for causing the associated transmitting apparatus to transmit a, radio sgnsi characteristic of the identity of the piane, means at the ground station governed by the associated receiving apparatus for stopping operation oi' said scanning means during transmission from said piane, communication means associated with said ground station and governed in part by seid associated receiving apparatus and in part by said scanning means for transmitting to a distant station e. code characteristic of the identity of said plane, the altitude of said piane end the identity of.' said ground station, and means on seid plane governed by the associated apparatus for preventing a subsequent operation oi the transmitting apparatus in response to the reception of a radiation characteristic of its a1- 'titude for a predetermined limited time.

SmGWICK N. WEGHT. @SCAR S. I itl REFEBENQES (EXETER) The ioiiowns references are oi record in the 21e of this patent:

governed by its essocisted recei apv Number 22 UNTED STATES PAWNTS Name Date Marshall June 17, 1941 Muilerheim Jan. 27, 1992 Hershey Mar. 3, 1942 Smith Feb. 9, 1932 Muether July 14, 1942 Hammond Mar. 13, 1934 Lesh Jan. 21, 1936 Wiiiiams Aug. 25, 1936 Sperry Mar. 4, 1930 Finnegan Apr. 13, 1943 Janssen Nov. 18, 1941 Culbertson Oct. 1, 1940 Brown Mar. 12, 1907 Hershey Apr, 30, 1935 Brixner Dec. 30, 1935 Ermes Dec. 23, 1930 Buckley Jan. 10, 1933 Piastino Aug. 29, 1939 Luck Aug. 12, 1941 Dunmore May 9, 1939 Kerr Feb. 16, 19113 Hershey Sept. 28, 1993

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